1. Field of the Invention
The present invention relates to an LLC serial resonant converter applied in a switch power supply, and more particularly to a double-output half-bridge LLC serial resonant converter.
2. Description of the Prior Art
Recently, switch power supplies are well-developed and well-used, and most of the switch power supplies are two-stage circuit framework. Please refer to FIG. 1, which illustrates a framework diagram of a conventional switch power supply. As shown in FIG. 1, the conventional switch power supply 1′ consists of a rectifying unit 11′, a power factor correction unit 12′, a DC/DC converting unit 13′, an output unit 14′, a PFC controlling unit 15′, and a convertor controlling unit 16′. The power factor correction unit 12′ is primary stage circuit, which is usually a boost converter and used for making the input current and the input voltage in phase, so as to make the power factor approach to 1. The DC/DC converting unit 13′ is secondary stage circuit and used for transforming the 390V voltage to the necessary voltage of the output unit 14′ (i.e., load end).
In the early days, the hard switching technology used in the power supply tends to cause switching losses when power switched is switched; moreover, the switching loss would increase with the increase of the switch frequency, and that brings the problems of low conversion efficiency, hard to do heat dissipation and inducing electromagnetic interference to the converting circuit. Accordingly, soft switching technology is developed and proposed for solving the problems induced by hard switching technology. To carry out the soft switching, at least one resonant inductor and at least one resonant capacitor is added into the converting circuit for constituting a resonator; Therefore, when the power switch is switched, the voltage signal crossed on the two terminals of the power switch is transformed to a sine wave voltage or a sine wave current by the resonator, so as to complete a zero voltage switching or a zero current switching. So that, the soft switch technology can not only solve the switching loss but also be helpful to the miniaturization of the converting circuit.
Currently, resonators are mainly divided into series resonant converter (SRC), parallel resonant converter (PRC), series-parallel resonant converter (SPRC) and LLC series resonant converter (LLC SRC), wherein the LLC SRC is proposed by C. Q. Lee and R. Liu in 1988.
Although there has a variety of resonant converters for applying in the switch power supplies; however, the current switch power supplies still have the shortcomings and drawbacks as follows:
1. There exists unbalance load current in the conventional switch power supply, and the unbalance load current would cause output voltage cross regulation in the output end of the switch power supply.
2. Inheriting to above point 1, although the hard switching technology and post regulator are used in the conventional switch power supply for enhancing the output load regulation, the load regulation in such switch power supply is still insufficient.
3. In addition, although LLC SRC performs higher low-frequency gain and provides wider input voltage range; however, the no-load or light-load output voltage still cannot be normally modulated whatever in LLC SRC or SRC, and that results in large voltage deviation.
Thus, in view of the conventional switch power supply and the resonators thereof still have shortcomings and drawbacks, the inventor of the present application has made great efforts to make inventive research thereon and eventually provided a double-output half-bridge LLC serial resonant converter.